LDR & Relay-Based Street Light Controlling DIY STEM KIT Science Project Model (Assembled), 100% Tested

Abstract:

The LDR & Relay-based Street Light Controlling circuit is designed using a light-dependent resistor (LDR), comparator IC LM393, and relay. The LDR acts as a light intensity detector, while the LM393 serves as a comparator. In the absence of light, no light falls on the LDR, causing the sensor to stop conducting, thereby activating the street light. When light falls on the LDR, the sensor conducts, turning the street light off.

Application of the Circuit:

Most LDR-based circuits available on the market use specialized LDRs, increasing costs and requiring complex circuitry. This LDR-based circuit uses readily available components to reduce complexity and cost. The LDR & Relay-based Street Light Controlling circuit detects light interruption and automatically turns on the street light in low-light conditions. The system continues to glow, indicating the absence of light, until light falls on the LDR again.

Why This Particular Circuit:

LDR-based light detection simplifies light intensity adjustment by using manual interruption, like covering the LDR with a hand palm. The circuit operates on a 5V DC supply, which can be obtained through a DC supply cable.

Explaining the Working of the Circuit:

The circuit’s basic idea is to turn on the street light in the absence of light. The LDR, a photoelectric device, converts light energy into electric energy. The LM393 comparator IC receives input from the LDR, controlling the relay switch. In normal conditions, when light falls on the LDR, the street light remains off. In low-light conditions, the relay activates, disconnecting the normally closed contact and connecting the normally open contact, thereby turning on the street light.

Building the Kit:

First, thoroughly read the manual, circuit diagrams, and study the supplied PCB and components. Ensure components are soldered correctly according to their positions on the PCB. The resistor values can be identified through color coding, and capacitor values are usually specified numerically. For ICs, use sockets for easy mounting/dismounting during troubleshooting.
Start soldering from the leftmost corner of the PCB, ensuring correct polarity, particularly for diodes and capacitors. Components with long leads, such as capacitors and transistors, should be soldered last.

Testing the Kit:

After assembling the components, connect a 5V DC power source. For testing, manually cover the LDR to block light. The red LED will glow, and the green LED will remain off. Adjust the resistive value of R2 (variable resistor) to set the desired light intensity. Once complete, install the unit at a street light location.

ICs Used:

LM393 – A dual differential comparator IC, widely used in street light control circuits.

Part List:

• Semiconductors:
  • U1 – LM393 (8-pin)
• Resistors (all 5% carbon):
  • R2 – 10k Ohm (variable)
  • R3, R4 – 1k Ohm
  • R5, R6 – 10k Ohm
• Capacitor:
  • C1 – 1uF
• Miscellaneous:
  • D4 – LDR
  • D1 – Red LED
  • D2 – Green LED
  • 5V USB cable
  • PCB
  • Relay

Key Applications:

Widely used in electronics, automation, robotics, and educational projects. Optimized for reliable performance in Indian-specific environments and conditions.

Keywords

• LDR & Relays Street Light Controlling DIY STEM KIT (Assembled)
• Electronic components India
• Street light control STEM kit
• LDR relay-based automation
• Buy LDR relay street light kit online